1. Field of the Invention
This invention generally relates to switches, and more particularly, to a switch that is mechanically driven and electrically coupled.
2. Description of the Related Art
In recent years, mobile telephones and mobile information terminals have become widespread very fast, with the advancements of the mobile communications systems. For instance, high frequency ranges such as 800 MHz to 1.0 GHz and 1.5 GHz to 2.0 GHz are used for the mobile telephones. High-frequency switches are for use in the devices in the above-described mobile communications systems. Miniaturization and power saving are demanded for the high-frequency switches. Conventionally, semiconductor switches that include gallium arsenide (GaAs) or the like have been employed. The semiconductor switches, however, lead to a large power loss and a low isolation. For these reasons, the development is in progress for radio frequency MEMS switches (hereinafter, referred to as RF MEMS SW) by use of the technology of microelectromechanical system (MEMS) that enables high isolation.
In Japanese Patent Application Publication No. 2004-200008 (hereinafter, referred to as Document 1) and Japanese Patent Application Publication No. 2005-243576 (hereinafter, referred to as Document 2), there are disclosed RF MEMS SWs whereby switching is done by electrically connecting or disconnecting one contact provided at a movable member with the other contact of a stationary member. In such RF MEMS SW, opening and closing of the switch while current is being applied (hereinafter, referred to as hot switching) consumes electricity at the contacts and generates heat at the contacts, resulting in damage. Approximately 10 mW is the power that can be used in hot switching. Therefore, after the applied current is turned off, the switch is opened and closed (hereinafter, referred to as cold switching). However, opening and closing of the applied current have to be done in synchronization with RF MEMS SW for cold switching, causing a complicated control.
In order to enable hot switching, as disclosed in Document 1, for example, there is provided a configuration in which resistors are arranged in series with multiple contacts connected in parallel. Also, as disclosed in Yonezawa et al., Fabrication Process of Non Arcing Power MEMS Relay, in the Technical Report of IEICE, The Institute of Electronics, Oct. 21, 2004 (hereinafter, referred to as Document 3), a configuration of FIG. 1 is shown. Referring now to FIG. 1, contact switches SW1 through SW5 are connected in parallel with a power supply E and a load-resistor RL, and resistors R1 through R4 are respectively connected in series with the contact switches SW2 through SW5. There is no resistor connected to the contact switch SW1. With such configuration, when the switches are turned on, the contact switches SW2 through SW5 are in a contact state and the contact switch SW1 is then in a contact state. By contrast, when the switches are turned off, the contact switch SW1 is in a non-contact state and the contact switches SW2 through SW5 are then in a non-contact state. The afore-described operation is known to improve power durability when the switch is opened and closed while direct current is being applied, as disclosed in Document 3.
Time control is necessary for multiple contact switches in a simple method in order to accomplish hot switching in RF MEMS SW which miniaturization is demanded, by use of the methods described in Document 1 and Document 3. Neither Document 1 nor Document 3, however, disclose a specific configuration, whereby the time control for multiple contact switches is accomplished by a simple method.